Dynamoelectric high-voltage machines and/or high-voltage systems, such as electrical generators in power plants, represent capital intensive installations, and require a high availability in order to be operated as economically as possible. One expedient for enhancing the availability of generators is early detection of impending damage in the individual system parts. The extent of possible damage can be limited by timely detection of an impending fault, it being possible to avoid severe damage to the generator, as well as to avoid unscheduled down times.
It is known that faults in electrical systems or system components make themselves known well before the occurrence of the actual damage by forming partial discharges or break sparks. Accordingly, it is common to monitor power plant generators, either continuously or at regular intervals to identify the occurrence of partial discharges that could be indicative of impending component failure. This mode of operation permits reliable early detection of faults in electrical equipment.
In a partial discharge monitor currently implemented in power plants, partial discharge pulses are detected and quantified using two passive partial discharge couplers on each isophase bus, one coupler located adjacent to the generator and one coupler located adjacent to a step-up transformer. Alarms are issued based on total detected pulse activity that includes pulses from all sources, that is, from the entire plant, not just from within the generator. These monitors can not distinguish partial discharge pulses with regard to “point of origin”. Typically, an expert on partial discharge analysis must then be sent to a site, i.e., a location in the power plant where partial discharge pulses have been sensed, and the expert must manually perform “time-of-flight” (TOF) analysis on a few of these pulses to determine the origin of the pulses.
In a TOF analysis, data captures at the generator and step-up transformer ends of the isophase bus are performed simultaneously. Two high speed digitizing circuits filter and capture decoupled high frequency partial discharge bus coupler signals at each bus site. Test personal must then switch the instrument to the next pair of isophase couplers and repeat data capture and analysis. Two high speed digitizing circuits may be used sequentially to reduce cost. A far better analysis is achieved when six such circuits are used to support simultaneous capture at all six sites. It is difficult to determine how many of these pulses are coming from the generator since clearly not all of the pulses can be manually tested in this manner. In many cases partial discharge activity is generated from sites other than the generator, posing no immediate threat to the plant and thus represents a false alarm.
Accordingly, there is a need for a method and monitor system for determining the location of partial discharge activity detected in an electrical conductor associated with a power plant generator. In particular, it is desirable to filter out partial discharge activity detected in a conductor that does not emanate from a generator.